Method for producing polyetherpolyols in the presence of a multimetal cyanide complex catalyst

ABSTRACT

Polyetherpolyols are prepared by reacting diols or polyols with ethylene oxide, propylene oxide, butylene oxide or a mixture thereof in the presence of a multimetal cyanide complex catalyst by a process which is carried out in a vertical, highly cylindrical reactor having a central stirrer and having heat exchanger plates through which a heat-exchange medium flows and which are arranged essentially in the longitudinal direction of the reactor, at an angle α of from 0 to 70° C. in the direction of rotation of the stirrer relative to the reactor radius.

[0001] The present invention relates to a process for the preparation ofpolyetherpolyols.

[0002] Polyetherpolyols are provided in large amounts, in particular forthe preparation of polyurethane foams. The known processes for thepreparation of polyetherpolyols are carried out as a rule from alkyleneoxide in the presence of a short-chain initiator with the use ofdifferent catalysts, such as bases, water-repellent double-layerhydroxides, acidic or Lewis acid systems, organometallic compounds ormultimetal cyanide complexes.

[0003] Heterogeneous multimetal cyanide complex catalysts are highlyselective and active catalysts which are suitable in particular for thepreparation of flexible-foam polyetherpolyols, where a high molecularweight has to be reached and long oxyalkylation times are required. Byusing multimetal cyanide complex catalysts, the production costs can bereduced and at the same time high-quality polyetherpolyol which can befurther processed to give polyurethane foams which have little odor andare therefore of high quality can be obtained. The literature disclosesthat secondary reactions which can lead to the formation of odoroussubstances and unsaturated components scarcely occur.

[0004] However, the high activity has the result that the heat ofreaction can no longer be removed in conventional reactors. If thepolyetherpolyol preparation catalyzed by a multimetal cyanide complex iscarried out in standard stirred kettles, the metering rates of alkyleneoxide are limited by the heat removal rate of the heat exchanger.

[0005] U.S. Pat. No. 5,811,595 proposes an ideally mixed reactorcomprising one or two heat exchangers, the polyetherpolyol being fedinto the circulation stream of the heat exchanger and the ethylene oxideinto the reactor. Mixing of the ethylene oxide with the liquid phase isachieved by means of a nozzle.

[0006] Disadvantages of this process are the high circulation raterequired for maintaining the high heat removal rate and the danger ofmechanical damage to the heterogeneous catalyst by the pump. Moreover,the highly reactive ethylene oxide is introduced into the reactor inwhich, owing to the cooling collars used, the heat removal is very poor,in particular at low fill levels, because of the small exchange area.Overheating owing to the high reaction rate, resulting in damage to theproduct, can occur. This may be increased by the poor mixing in thereactor.

[0007] EP-A-0 850 954 describes a process in which the reaction takesplace in the gas space above the reaction liquid. The polyetherpolyol iscirculated via a heat exchanger and fed in through nozzles. This resultsin a large liquid surface. Simultaneously with this, ethylene oxide andpolyetherpolyols are metered in via nozzles. The large surface resultsin good mass transfer and hence high reaction rates.

[0008] Owing to the high reaction rate which can be achieved with thisprocess, local excess temperatures are likely in the individual dropletsand in turn may result in damage to the product. Furthermore, here toothe high circulation rate required for heat removal is not withoutproblems for the heterogeneously dispersed multimetal cyanide complexcatalyst; the danger of damage cannot be ruled out.

[0009] The artificially enlarged gas phase is a further potentialdanger, in particular in the ethoxylation, since free alkylene oxide ispresent in the gas phase. Ethylene oxide tends to gas-phasedecomposition, which can lead to bursting of the reactor. On the otherhand, when the polyetherpolyol or ethylene oxide is passed into theliquid, rapid reaction of the alkylene oxide is to be expected owing tothe active multimetal cyanide complex.

[0010] EP-B-0 633 060 discloses a reactor for gas-liquid reactions whichcomprises a central stirring apparatus, around which heat exchangerplates through which a heat-exchange medium flows are arranged at anangle from 0 to 70° in the direction of rotation of the stirrer relativeto the reactor radius. As a result of the direct heat removal at thepoint of heat generation, higher productivity, a high product qualityand reduced catalyst consumption can be ensured. The reactor EP-B-0 633060 was proposed in particular for highly exothermic catalytichydrogenation reactions.

[0011] It is an object of the present invention to provide a processwhich employs a simple apparatus for the preparation of polyetherpolyolsin the presence of multimetal cyanide complex catalysts with improvementof the space-time yield and avoidance of local overheating and hence ahigher level of secondary reactions, thus ensuring a high productquality.

[0012] We have found that this object is achieved by a process for thepreparation of polyetherpolyols by reacting diols or polyols withethylene oxide, propylene oxide, butylene oxide or a mixture thereof inthe presence of a multimetal cyanide complex catalyst.

[0013] In the invention, the reaction is carried out in a vertical,highly cylindrical reactor having a central stirrer and having heatexchanger plates through which a heat-exchange medium flows and whichare arranged essentially in the longitudinal direction of the reactor,at an angle α of from 0 to 70° in the direction of rotation of thestirrer relative to the reactor radius.

[0014] The vertical, highly cylindrical reactor described in EP-B-0 633060 and having a central stirrer and having heat exchanger platesthrough which a heat-exchange medium flows and which are arrangedessentially in the longitudinal direction of the reactor, at an angle ofα of from 0 to 70° in the direction of rotation of the stirrer relativeto the reactor radius was developed in particular for highly exothermiccatalytic hydrogenation reactions. These involve low-viscosity liquidreaction mixtures, i.e. liquids which have a viscosity substantiallybelow 10 mPa.s under reaction conditions.

[0015] In contrast, the inventors of the present process havesurprisingly found that the reactor type disclosed in EP-B-0 633 060 canalso be used for reaction media having a higher viscosity, such as thepolyetherpolyols of the present invention. As a rule, polyetherpolyolshave high viscosities, about in the range from 80 to 1000 mPa.s at roomtemperature and still above 20 mPa.s, frequently above 100 mPa.s, underreaction conditions (from about 100 to 130° C.). It is known that theboundary layer between heat exchanger and reaction mixture increaseswith increasing viscosity, with the result that the heat is increasinglypoorly removed. According to the novel process, sufficient heat removalcould be achieved in spite of the increased viscosity, so that highalkylene oxide metering rates could be realized, resulting in animproved space-time yield and hence higher productivity and a goodproduct quality. Local excess temperatures which might lead to damage tothe product were avoided.

[0016] According to the invention, diols or polyols are initially takentogether with a multimetal cyanide complex catalyst in a vertical,highly cylindrical reactor having a central stirrer and having heatexchanger plates through which a heat-exchange medium flows and whichare arranged essentially in the longitudinal direction of the reactor,at an angle α of from 0 to 70° C. in the direction of rotation of thestirrer relative to the reactor radius, and are then reacted withethylene oxide, propylene oxide, butylene oxide or a mixture thereof.After the alkylene oxide has completely reacted, the reaction product isremoved from the reactor.

[0017] The invention does not include any restrictions with regard tothe multimetal cyanide complex catalyst which may be used; it may havean amorphous form but preferably has an at least partially,predominantly or completely crystalline form. If required, the catalystis supported. Particularly preferably used multimetal cyanide complexcatalysts are those of the formula (I)

M¹ _(a)[M²(CN)_(b)L¹ _(c)]_(d)·e(M¹ _(f)X_(g))·hL².iH₂O  (I)

[0018] where

[0019] M¹ is at least one element from the group consisting of Zn(II),Fe(II), Co(III), Ni(II), Mn(II), Co(II), Sn(II), Pb(II), Fe(III),Mo(IV), Mo(VI), Al(III), V(IV), V(V), Sr(II), W(IV), W(VI), Cu(II),Cd(II), Hg(II), Pd(II), Pt(II), V(III), Mg(II), Ca(II), Sr(II), Ba(II)and Cr(III),

[0020] M² is at least one element from the group consisting of Fe(II),Fe(III), Co(III), Cr(III), Mn(II), Mn(III), Ir(III), Rh(III), Ru(II),V(IV), V(V), Co(II) and Cr(II),

[0021] L¹ is at least one ligand from the group consisting of cyanide,carbonyl, cyanate, isocyanate, nitrile, thiocyanate and nitrosyl,

[0022] X is a formate anion, acetate anion or propionate anion,

[0023] L² is at least one water-miscible ligand from the groupconsisting of alcohols, aldehydes, ketones, ethers, polyethers, esters,urea derivatives, amides, nitriles and sulfides,

[0024] a, b, d, e, f and g are integers or fractions greater than zero,c, h and i are integers or fractions greater than or equal to zero, a,b, c and d being chosen so that the electroneutrality condition isfulfilled and

[0025] f and g being chosen so that the electroneutrality condition isfulfilled, whose X-ray diffraction pattern has reflections at at leastthe d values

[0026] 6.10 Å±0.004 Å

[0027] 5.17 Å±0.04 Å

[0028] 4.27 Å±0.02 Å

[0029] 3.78 Å±0.02 Å

[0030] 3.56 Å±0.02 Å

[0031] 3.004 Å±0.007 Å

[0032] 2.590 Å±0.006 Å

[0033] 2.354 Å±0.004 Å

[0034] 2.263 Å±0.004 Å

[0035] if X is a formate anion, whose X-ray diffraction pattern hasreflections at at least the d values

[0036] 5.20 Å±0.02 Å

[0037] 4.80 Å±0.02 Å

[0038] 3.75 Å±0.02 Å

[0039] 3.60 Å±0.02 Å

[0040] 3.46 Å±0.01 Å

[0041] 2.824 Å±0.008 Å

[0042] 2.769 Å±0.008 Å

[0043] 2.608 Å±0.007 Å

[0044] 2.398 Å±0.006 Å

[0045] if X is an acetate anion, and whose X-ray diffraction pattern hasreflections at at least the d values

[0046] 5.59 Å±0.05 Å

[0047] 5.40 Å±0.04 Å

[0048] 4.08 Å±0.02 Å

[0049] 3.94 Å±0.02 Å

[0050] 3.76 Å±0.02 Å

[0051] 3.355 Å±0.008 Å

[0052] 3.009 Å±0.007 Å

[0053] 2.704 Å±0.006 Å

[0054] 2.381 Å±0.004 Å

[0055] if X is a proprionate anion or which have a monocinic crystalsystem if X is an acetate anion.

[0056] Such multimetal cyanide complex catalysts are described inDE-A-197 42 978.

[0057] According to the invention, the process is carried out in avertical, highly cylindrical reactor having a central stirrer and havingheat exchanger plates through which a heat-exchange medium flows andwhich are arranged essentially in the longitudinal direction of thereactor, at an angle α of from 0 to 70° C. in the direction of rotationof the stirrer relative to the reactor radius. Such a reactor isdescribed in EP-B-0 633 060, preferably for highly exothermichydrogenation reactions.

[0058] The multimetal cyanide complex catalyst is preferably used inamounts of less than 250 ppm, particularly preferably less than 100 ppm,in particular less than 50 ppm, based on the mass of product to beproduced. In reactors equipped with heat exchanger plates, there is thedanger that heterogeneous catalysts would be deposited in corners,angles or other areas with insufficient flow and will consequently beavailable only in an insufficient amount, if at all, for the catalyticreaction. This problem is not so critical at relatively high catalystconcentrations because a catalyst loss in this case does not have anyextreme effect on the quality of the catalysis and of the products. Onthe other hand, at low catalyst concentrations, for example 100 ppm orless, the loss of available catalyst, even in an order of magnitude of afew 10 ppm, means a dramatic absolute loss of catalyst material andhence of catalyst activity. The result is substantially poorer productquality, broader molecular weight distributions and high molecularweight fractions. In contrast, it was surprisingly found that, in thenovel process, such problems, did not occur in spite of very lowcatalyst concentrations and the high viscosity of the polyol, and nodeterioration in the product quality took place.

[0059] In a preferred embodiment, the heat exchanger plates are bent orcurved in the direction of rotation of the stirrer. This reduces themechanical resistance.

[0060] A preferably used heat-exchange medium is water.

[0061] According to a preferred embodiment, the heat-exchange medium ispassed from the heat exchanger plates in a loop flow via a heatexchanger arranged outside the reactor. Consequently, the heat removalcan be additionally improved.

[0062] In order to ensure heat removal in the case of small amounts ofinitiator and to permit heating-up of the initiator, in particular atthe beginning of the reaction, a further heat exchanger may also bearranged on the outer jacket of the reactor.

[0063] The heat exchanger arranged on the outer jacket of the reactor ispreferably in the form of heat exchanger half-tubes.

[0064] The reaction is preferably carried out at from 90 to 200° C. andfrom 1 to 50 bar.

[0065] A temperature range of from 110 to 140° C. and a pressure of from2 to 10 bar are particularly preferred.

[0066] The reaction is preferably carried out by the semibatchprocedure, i.e. initiator and catalyst are initially taken and thealkylene oxide, i.e. ethylene oxide, propylene oxide, butylene oxide ora mixture thereof, is metered into the reactor until the desired molarmass is reached. This ensures that, on the one hand, there is noaccumulation of alkylene oxide and hence the danger of a runawayreaction is avoided and, on the other hand, safe temperature control isachieved. Thus, exact control of the residence time required forconstant molecular weight distribution can be achieved.

[0067] By introducing stirring energy via the central stirrer, thoroughmixing of all components of the reaction mixture is achieved. Thearrangement of the heat exchanger plates in the reactor at an angle α offrom 0 to 70° in the direction of rotation of the stirrer relative tothe reactor radius leads to virtually complete freedom from a reactiontemperature gradient over the reactor. Consequently, local overheatingis avoided, resulting in a substantial suppression of secondaryreactions and substantial avoidance of catalyst deactivation.Accordingly, high space-time yields are achieved, which are attributableto the good heat removal and the high alkylene oxide metering rate thuspossible.

[0068] The invention is explained in more detail below with reference toan embodiment:

[0069] The following methods of determination were used:

[0070] The content of unsaturated components was determined via theiodine number. For this purpose, in a first process, the unsaturatedfractions were brominated and excess bromine was reacted with potassiumiodide solution with precipitation of iodine. The content of unsaturatedcomponents in milliequivalents/g (meq/g) was obtained by titrating theprecipitated iodine with thiosulfate solution. The cycloacetal contentwas determined by headspace GC-MS analysis, the mass trace of m/e=130being monitored. The sample temperature was 130° C.

Comparative Example

[0071] An initiator (glyceryl propoxylate) having an average molar massof 400 g/mol was initially taken in a stirred kettle having internalcooling coils. 100 ppm, based on the final polyol mass, of DMC wereadded.

[0072] The preparation of the multimetal cyanide catalyst was carriedout in a two-stage process, in which first the acid and then thecatalyst was obtained by precipitation. For this purpose, 7 1 ofstrongly acidic ion exchanger which was in the sodium form, i.e.Amberlite® 252 Na from Rohm & Haas, were filled into an exchanger columnhaving a length of 1 m and a volume of 7.7 1. The ion exchanger was thenconverted into the acid form by passing 10% strength hydrochloric acidat a rate of 2 bed volumes per hour over the exchanger column for 9hours until the sodium content in the discharge was <1 ppm. The ionexchanger was then washed with water. The regenerated ion exchanger wasthen used for preparing an essentially alkali-free hexacyanocobalticacid. For this purpose, a 0.24 molar solution of potassiumhexacyanocobaltate in water was passed over the ion exchanger at a rateof one bed volume per hour. After 2.5 bed volumes, the potassiumhexacyanocobaltate solution was replaced with water. The 2.5 bed volumesobtained had on average a content of 4.5% by weight of hexacyanocobalticacid and alkali contents of <1 ppm.

[0073] For the preparation of the catalyst, 8553.5 g of zinc acetatesolution (content of zinc acetate dihydrate: 8.2% by weight, content ofPluronic® PE 6200, i.e. a block copolymer of ethylene oxide andpropylene oxide, which is used for controlling the crystal morphology:1.3% by weight) were then initially taken in a 20 1 reactor and heatedto 60° C. while stirring. 9956 g of hexacyanocobaltic acid solution(cobalt content 9 g/l, content of Pluronic® PE 6200 1.3% by weight) wasthen added in the course of 20 minutes at 60° C. with constant stirring.The suspension obtained was stirred for a further 60 minutes at 60° C.Thereafter, the solid thus obtained was filtered off and was washed with6 times the cake volume. The moist filter cake was then dispersed inpolypropylene glycol having a molar mass of 400 g/mol.

[0074] The dispersion thus obtained was used as the catalyst.

[0075] Dewatering was carried out for 1 hour under reduced pressure,after which propoxylation was effected until a molar mass of 3000 g/molwas reached. A space-time yield of 210 kg/m³/h was obtained from thefeed rate of the propylene oxide, which was limited only by the heatremoval rate. A content of unsaturated components of 0.0052 meq/g wasfound. The content of cycloacetals was 0.06 ppm.

EXAMPLE

[0076] The reaction was carried out under the same experimentalconditions as in the Comparative Example, but in a cylindrical reactorhaving a central stirrer with heat exchanger plates through which waterflows and which were arranged in the longitudinal direction of thereactor and radially in the reactor. The reactor had a capacity of 40 tand the heat-exchange area was 600 m². As a result of the improved heatremoval, the feed rate of the propylene oxide could be increased by afactor of 1.8 and consequently the space-time yield could be increasedto 380 kg/m³/h. The contents of unsaturated components and cycloacetalswere determined as 0.0050 meq/g and 0.04 ppm, respectively.

[0077] Thus, by using the novel reactor, it was possible to achieve anincrease of 80% in the space-time yield with slightly improved productquality.

We claim:
 1. A process for the preparation of polyetherpolyols by reacting diols or polyols with ethylene oxide, propylene oxide, butylene oxide or a mixture thereof in the presence of a multimetal cyanide complex catalyst, wherein the reaction is carried out in a vertical, highly cylindrical reactor having a central stirrer and having heat exchanger plates through which a heat-exchange medium flows and which are arranged essentially in the longitudinal direction of the reactor, at an angle α of from 0 to 70° in the direction of rotation of the stirrer relative to the reactor radius.
 2. A process as claimed in claim 1, wherein the heat exchanger plates are arranged radially.
 3. A process as claimed in claim 1 or 2, wherein the multimetal cyanide complex catalyst is used in a concentration of less than 250 ppm, preferably less than 100 ppm, particularly preferably less than 50 ppm, based on the mass of product to be produced.
 4. A process as claimed in any of claims 1 to 3, wherein the heat exchanger plates are bent or curved in the direction of rotation of the stirrer.
 5. A process as claimed in any of claims 1 to 4, wherein the heat-exchange medium is passed from the heat exchanger plates in a loop flow via a heat exchanger arranged outside the reactor.
 6. A process as claimed in any of claims 1 to 5, wherein a heat exchanger is arranged on the outer jacket of the reactor.
 7. A process as claimed in claim 6, wherein the heat exchanger arranged on the outer jacket of the reactor is in the form of heat exchanger half-tubes.
 8. A process as claimed in any of claims 1 to 7, wherein the reaction is carried out at from 90 to 200° C. and from 1 to 50 bar.
 9. A process as claimed in claim 8, wherein the reaction is carried out at from 110 to 140° C. and from 2 to 10 bar.
 10. A process as claimed in any of claims 1 to 9, wherein the multimetal cyanide complex catalyst corresponds to the formula (I) M¹ _(a)[M²(CN)_(b)L¹ _(c)]_(d)·e(M¹ _(f)X_(g))·hL².iH₂O  (I)where M¹ is at least one element from the group consisting of Zn(II), Fe(II), Co(III), Ni(II), Mn(II), Co(II), Sn(II), Pb(II), Fe(III), Mo(IV), Mo(VI), Al(III), V(IV), V(V), Sr(II), W(IV), W(VI), Cu(II), Cd(II), Hg(II), Pd(II), Pt(II), V(III), Mg(II), Ca(II), Sr(II), Ba(II) and Cr(III), M² is at least one element from the group consisting of Fe(II), Fe(III), Co(III), Cr(III), Mn(II), Mn(III), Ir(III), Rh(III), Ru(II), V(IV), V(V), Co(II) and Cr(II), L¹ is at least one ligand from the group consisting of cyanide, carbonyl, cyanate, isocyanate, nitrile, thiocyanate and nitrosyl, X is a formate anion, acetate anion or propionate anion, L² is at least one water-miscible ligand from the group consisting of alcohols, aldehydes, ketones, ethers, polyethers, esters, urea derivatives, amides, nitriles and sulfides, a, b, c, d, e, f, g, h and i are integers, a, b, c and d being chosen so that the electroneutrality condition is fulfilled and f and g being chosen so that the electroneutrality condition is fulfilled, whose X-ray diffraction pattern has reflections at at least the d values 6.10 Å±0.004 Å 5.17 Å±0.04 Å 4.27 Å±0.02 Å 3.78 Å±0.02 Å 3.56 Å±0.02 Å 3.004 Å±0.007 Å 2.590 Å±0.006 Å 35 2.354 Å±0.004 Å 2.263 Å±0.004 Å if X is a formate anion, whose X-ray diffraction pattern has reflections at at least the d values 5.20 Å±0.02 Å 4.80 Å±0.02 Å 3.75 Å±0.02 Å 3.60 Å±0.02 Å 3.46 Å±0.02 Å 2.824 Å±0.008 Å 2.769 Å±0.008 Å 2.608 Å±0.007 Å 2.398 Å±0.006 Å if X is an acetate anion, and whose X-ray diffraction pattern has reflections at at least the d values 5.59 Å±0.05 Å 5.40 Å±0.04 Å 4.08 Å±0.02 Å 3.94 Å±0.02 Å 3.76 Å±0.02 Å 3.355 Å±0.008 Å 3.009 Å±0.007 Å 2.704 Å±0.006 Å 2.381 Å±0.004 Å if X is a proprionate anion or which have a monoclinic crystal system if X is an acetate anion.
 11. A process as claimed in any of claims 1 to 10, wherein the multimetal cyanide complex catalyst is substantially or completely crystalline.
 12. A process as claimed in claim 11, wherein a multimetal cyanide complex catalyst of the zinc-cobalt type is used. 